This application outlines a research based approach to determining the cellular mechanisms involved in the loss of basal forebrain cholinergic neurons (BFCN) commonly associated with Down syndrome (DS) and Alzheimer's disease (AD). The goal of the proposed research is to understand the mechanisms involved in disease related failure of nerve growth factor (NGF) signaling leading to the consecutive loss of BFCNs. Ultimately this line of investigation will assist the development of strategies for preventing or bypassing BFCN degeneration and associated cognitive decline. Specific aims are designed to measure rates of NGF signaling endosome retrograde transport in cultured BFCN axons, and to determine the mechanisms underlying transport defects using DS and AD mouse models. The culturing of dissociated BFCNs in micro fluidic chambers will allow for separation of cell bodies from axons in diffusion limited compartments. Individual axons can be visualized as they grow along microgrooves etched into the glass between the two chambers. Adding NGF to the axonal chamber results in its receptor binding, internalization and retrograde transport to cell bodies thereby mediating BFCN survival. Retrograde transport of signaling endosomes will be visualized in real time with high signal to noise ratio by the employing NGF conjugated to quantum dots. Evidence to date supports a model for increased gene dosage of APR being involved in NGF transport defects and loss of BFCNs either via increased production of A[unreadable] or other proteolytic fragments of APP such as the C-terminal fragment. Individuals with DS typically develop senile plaques and neurodegeneration characteristic of AD in their early to mid 40's, attributed in part to the presence of a third copy of the amyloid precursor protein (APP) found on chromosome 21. Proteolytic cleavage of APP can lead to production of the amyloid beta (A[unreadable]) peptide responsible for the senile plaque deposition, neurodegeneration and potentially involved in early cognitive decline associated with amyloidopathies. As the U.S. population ages the incidence of AD is projected to increase from the current 5 million to an estimated 15 million diagnosed cases by the year 2050 and Medicare costs are expected to rise from $91 billion in 2005 to $160 billion by 2010. Delaying the age of onset by as little as 5 years may alleviate a majority of the socio-economic burden as well individual suffering associate with dementia. In addition the quality of life and level of independence for individuals living with DS or AD would increase by extending the number of years without before the onset of neurodegeneration.